Absence of explicit and implicit memory under general anaesthesia using TCI of propofol.

AUTHORS : Lequeux PY, Barvais L, Cantraine F, Hennart D, Levarlet M.

AFFILIATION : Department of Anaesthesiology, Erasmus hospital, Free University of Brussels, Belgium. (Route de Lennik, 808. 1070 Brussels. Tel.: 32 / 2 / 5553324)

Background & goal of study

Episodes of explicit or implicit memory have been associated with postoperative sequels¹. TCI of propofol using the “Diprifusor” system is now frequently used during total intravenous anaesthetic technique. Therefore, we decided to study explicit or implicit memory during general anaesthesia using TCI of propofol.

Material & methods

After written and informed consent, twenty ASA I patients, aged less than 50 and undergoing minor surgery were randomised in 2 groups : an experimental group (Group E) and a control group (Group C). In both groups, no patient was premedicated or received any benzodiazepine. Propofol was given to obtain loss of consciousness (LOC) by a progressive stepwise increase of 0.5 µg/ml of the theoretical target blood concentration using a Diprifusor system including the pharmacokinetic set of Marsh et al.². When LOC was obtained, the effect target concentration of propofol was maintained stable during the whole study period. Patients were ventilated by face mask with 100 % O₂. A tape containing 30 words repeated three-times was played either before the start of anaesthesia in group C or when LOC was obtained in group E. Thereafter, general anaesthesia was continued and supplemented by bolus of opioids and muscle relaxants as required. In both groups, 3 different tests of completion, evocation and recognition were performed at minimum 2 hours after full recovery to explore the explicit and implicit memories. Student T and Mann-Whitney tests were used for statistical analysis.

Results

Both groups were comparable concerning age, sex and duration of surgery. At LOC, theoretical effect concentrations of propofol were 2.8±0.7 µg/ml in group C, and 2.8±1.0 µg/ml in group E. Explicit and implicit memories were observed in group C. But none of the 3 tests showed any memory in group E (a statistical difference was observed between group E and C in the 3 tests: p<0.01).

Conclusions

In our group of young ASA I patients, neither explicit nor implicit memory were evidenced when the theoretical target effect concentration of propofol using a Diprifusor system was maintained at the level leading to LOC.

References

1. Ghoneim M, Block R. Anesthesiology.1997;87:387-410

2. Marsh B, White M, Morton N, et al. Br. J. Anaesth. 1991;67:41-